HCV Deliverable D2400.1 Technology Evaluation: engine fan, high

Responsible (Name, Organisation)
Nickolas Vlachos, APTL/CERTH
Page
DELIVERABLE REPORT
1(26)
Issuer (Name, Organisation)
Date
WP No
Report No
Tytus Adamczewski, Solaris Bus
May 2013
2400
D2400.1
Nickolas Vlachos, APTL/CERTH
Subject:
Dissem. Level
Technology Evaluation Report of Auxiliaries for Electric Fan, High-Power Generator and PU
Electrified Control of Crank Case Emissions
DELIVERABLE D2400.1
TECHNOLOGY EVALUATION REPORT OF
AUXILIARIES FOR ELECTRIC FAN, HIGHPOWER GENERATOR AND ELECTRIFIED
CONTROL OF CRANKCASE EMISSIONS
HCV Hybrid Commercial Vehicle – D2400.1, Rev_0
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Summary
The Sub-Project SP2000 is focused on the electrification of auxiliaries. The work package
WP2400, more specifically, covers the electrification of powertrain auxiliaries. These can
include the engine fan and the emission control system but also the high power generator,
which plays a central role in the electrification effort. In view of the increasing stringency in
vehicle emissions, consideration is also given to the crankcase emissions control device, a
minor component relative to the other auxiliaries mentioned both in terms of size and energy
consumption.
The first two sections of the current report presents a review of available technologies for the
high power generator and the engine fan for Diesel hybrid bus powertrains. This review of
the state of the art will feed forward to the selection and implementation of these auxiliaries
within subsequent tasks of WP2400. The final section of this report reviews potential
electrified solutions to reduce crankcase emissions, although this auxiliary is not part of the
WP2400 hardware implementation.
HCV Hybrid Commercial Vehicle – D2400.1, Rev_0
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Abbreviations
DPF
Diesel particulate filter
HPG
High Power Generator
HVDC
Hybrid Beltless Alternator
SAE
Society of Automotive engineers
NEC
National Electrical Code
UL
North American standard
HCV Hybrid Commercial Vehicle – D2400.1, Rev_0
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Introduction
Nowadays, more attention is paid on protecting the environment and therefore, reducing
emissions. Vehicles have to fulfill stricter emission norms, which is challenging for their
development as well as their production. Therefore, at the moment, it can be observed more
frequently that vehicles equipped with classical engines are replaced with vehicles that have
fully alternative or hybrid drives. After hybrid vehicles were introduced to the market, the idea
of the electrification of auxiliary devices in vehicles started to be discussed in the industry.
For buses this electrification is especially important because it influences the total amount of
energy consumed by the vehicle, which results from the high power need of the devices
installed on board. One of the most significant of these auxiliaries for buses is the
combustion engine’s cooling fan, for which electrification could lead to considerable powersaving benefits. This document presents an analysis of the solutions mentioned above. In
order to provide sufficient electrical power, needed to power the fan and other potentially
electrified auxiliaries, it is necessary to verify the implementation possibilities of the highpower generator. This would increase the capability of generating the needed current on the
bus and, thus, make the fan independent of the combustion engine’s rotational speed.
In hybrid vehicles, due to the high power necessary to assist the drive unit during
acceleration and the amount of energy released during vehicle braking, a 600 V voltage
system is also used additionally to the typical 24 VDC system for on board auxiliaries. The
use of such high voltage level enables decreasing the current flows in the systems to a level
of 200-400 A. In this way, it is possible to use power conductors with smaller diameters and
to increase the operational efficiency as well as the energy transmission of the systems.
In a hybrid vehicle there are two different types of in-built accumulators enabling storage of
electrical energy: the vehicle utilities/auxiliaries batteries and the traction batteries . The first
accumulator module is normally a 24 V on-board system, usually arranged using two 12 V
packages, each of them consisting of six 2 V cells placed in series. In buses, it is most
common to use maintenance-free lead-acid accumulators, which are shock-resistant due to
their reinforced design. Commonly used in buses and other utility vehicles are accumulators
with a capacity of 100-220 Ah. In order to start the IC engine of the bus, it is necessary to
provide proper rotational speed to the crankshaft. In vehicles equipped with classical
engines, this function is realised by a starter. In hybrid vehicles the combustion engine gets
started using the high-power electrical traction engine. The energy needed for the start-up is
obtained from the traction accumulators of the bus. Usually, hybrid vehicles are not equipped
with a classic starter.
It can be seen from the technical context described above, that further possibilities of
optimizing the energy efficiency and other operational enhancements can be investigated
within is the HCV project. The project’s aim is the development of urban buses and delivery
vehicles equipped with the advanced second generation of energy efficient hybrid electric
powertrains. The final result will be the demonstration of passenger buses and delivery
vehicle with this higher technology. The Sub-Project 2000 is very important in this effort
because electrification of auxiliaries has not been fully developed for the current hybrid
HCV Hybrid Commercial Vehicle – D2400.1, Rev_0
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systems. A larger degree of electrification of these components and an optimisation of the
control strategies would make it possible to improve fuel consumption and to include new
functionality.
As mentioned above, the work package WP2400 considers the electrification of powertrain
auxiliaries. These are components like the radiator fan and the high power generator, which
plays a main role in the effort of electrification. The emission control system, normally seen
as an integral part of the Diesel powertrain, is also considered in WP2400 as an auxiliary
within the context of investigating its electrification.
In beginning the hybrid powertrain potential assessment (with respect to fuel consumption), it
is important to have an overview of technologies that are relevant for the electrification of the
powertrain auxiliaries. The main part of the current report an overview of available
technologies for the high power generator and the engine fan components for Diesel hybrid
bus powertrains.
As with other auxiliaries considered, typical crankcase breathers use the engine to power
their operation: crankcase emissions are vented to the low pressure pre-turbo section of the
intake manifold thereby allowing clean air to be continuously brought into the crankcase.
This constitutes a minor energy expenditure for the vehicle. It is, nonetheless, interesting to
at least review technologies which show potential for an electrical solution for crankcase
emissions, even though this is not strictly of interest for hybrid vehicles only. Therefore, the
second part of this report reviews possible electrified systems for crankcase emissions and
discusses the motivation and/or benefits of their electrification, considering aspects beyond
just energy efficiency.
HCV Hybrid Commercial Vehicle – D2400.1, Rev_0
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Conclusions
Using the Vanner HVDC system using a DC Converter has many advantages compared to
the traditional alternator. The overall efficiency improves significantly and also the fuel
consumption and the exhaust gas emissions are reduced. The DC power is stable at all
temperatures and speeds. The voltage regulation is very exact and it does not need a lot of
maintenance and is constructed to be long lasting. Safety concerns that were related to the
alternators are eliminated due to the location of installation in the vehicle. By the usage of a
solid state DC-DC Converter downtime can be minimised by reducing parts of the vehicle,
that normally need extensive maintenance.
The use of hybrid drives in buses brings benefits like lower fuel consumption obtained due to
energy recovery during braking and also enables the possibility to electrify auxiliary devices.
For buses, this electrification is of major importance and influences the total amount of
energy consumed by the vehicle, as a consequence of the high power of the auxiliary
devices installed on board.
In general, it is expected that the electrified system higher efficiency and the enhanced
control of the electrical devices lead to directly measureable energy savings and higher
degree of freedom for maintaining the system.
The use of electric fans in the engine cooling system will help to reduce the fuel
consumption. This will happen because the electric fans are controlled by an external
controller and are 100% independent of the diesel engine work while the hydrostatic fan
always runs when the bus engine is running.
Reducing the number of mechanical power receivers in the combustion engine enables the
possibility to increase the power output and to reduce the fuel consumption while maintaining
the same operating conditions.
The electrification potential of crankcase emissions control devices was evaluated mainly out
of interest for other possible benefits besides energy efficiency due to the fact that the engine
blow-by, in general, is of much smaller volumetric flow rate than the main engine exhaust gas
and, on the whole, crankcase ventilation does not represent a significant power draw within
the powertrain. The survey conducted found one electrified crankcase gases cleaning
device, the cone-stack separator made by MAHLE GmbH, which has undergone extensive
development and is ready for commercial application. This electrified device also exhibits low
power requirement, to the point of being compatible with non-hybrid vehicles having
conventional electrical power availability on board. In terms of advantages over passive (nonelectrified) technologies for blow-by gases cleaning, the electrified system claims to avoid
situations where the operating conditions or negligent maintenance can lead to the blockage
of the porous materials that separate the emitted oil droplets in conventional devices. This
situation can result in numerous problems due to increased crankcase pressure and
inadequate crankcase ventilation. Furthermore, higher separation effectiveness is claimed,
this having benefits especially for engine intake components (turbo-charger, intake valves).
Therefore, the main targets for electrification and, in fact, most development on the
crankcase ventilation system, seem to be to improve oil mist retention performance, reduce
crankcase back pressure and improve robustness of the separator. Due to the small power
drain (parasitic or directly consumed) of crankcase gases oil mist separators, further energy
efficiency improvements are almost a non-issue and, therefore, further consideration was not
specified in the context of the HCV SP2000 as it is done for other major vehicle auxiliaries.
HCV Hybrid Commercial Vehicle – D2400.1, Rev_0
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Table of contents
Summary ............................................................................................................................... 2
Abbreviations ........................................................................................................................ 3
Introduction ........................................................................................................................... 4
Conclusions ........................................................................................................................... 6
Table of contents ................................................................................................................... 7
Table of figures...................................................................................................................... 8
List of tables .......................................................................................................................... 9
A.
B.
High Power Generator in Place of Alternators...............................................................10
A.1.
Installation of the high-power generator..................................................................13
A.2.
Advantages resulting from the use of a power generator – fuel savings .................14
A.3.
Cost Analysis .........................................................................................................15
Electric Fans in Place of a Hydrostatic Fan for Engine Cooling .....................................16
B.1.
C.
D.
Installation of the cooling system ............................................................................17
B.1.1.
Advantages resulting from the use of electric engine fan – fuel-savings ..........21
B.1.2.
Cost Analysis ..................................................................................................21
Potential for Electrification of the Crankcase Emissions Control ...................................22
C.1.
Scope of the review ................................................................................................22
C.2.
Crankcase emissions .............................................................................................22
C.3.
Existing commercial solutions for crankcase emissions control ..............................23
C.4.
Conclusions for the electrification of crankcase emission control............................24
References ...................................................................................................................26
HCV Hybrid Commercial Vehicle – D2400.1, Rev_0
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Table of figures
Figure A-1. Typical generator capacity depending on engine speed ........................ 10
Figure A-2. The installation of alternators in a typical bus ........................................ 11
Figure A-3. Scheme presenting the connection of the high-power generator to the
wiring system of a bus and the physical form of the Vanner generator (ref. [A-1]).
.......................................................................................................................... 12
Figure A-4. Mounting details for the high power generator (dimensions in inches) 0 13
Figure A-5. System efficiency and electrical stress reduction benefits .................... 14
Figure A-6. System efficiency mapping .................................................................... 14
Figure B-2. Single electrically driven DC fan module ................................................ 18
Figure B-3. Isolated rendering of the cooling system employing a hydrostatic driven
fan ..................................................................................................................... 18
Figure B-4. Isolated depiction of the complete cooling system installation with electric
fans.................................................................................................................... 19
Figure B-5. Performance map of the W3G 300-ER38-45 electric fan unit with respect
to suction pressure and achieved air flow rate (ref. [B-1]) ................................. 21
Figure C-1. The electrical cone stack separator by MAHLE [C-4] ............................ 24
HCV Hybrid Commercial Vehicle – D2400.1, Rev_0
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List of tables
Table 1. General specification of High Power Generator .......................................... 12
Table 2 - Comparison of electric fan models considered .......................................... 19
Table 3. Specifications of the electronically controlled fan........................................ 20
HCV Hybrid Commercial Vehicle – D2400.1, Rev_0
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A. High Power Generator in Place of Alternators
The alternator is the source of electrical energy during the operation of the combustion
engine on the bus. The alternator converts mechanical energy, received from the engine via
belt transmission, into electrical energy. This energy is used to power the electrical circuits in
the bus and to charge the 24 V on-board accumulators. The alternators used in buses are
alternating-current generators (see Figure A-1), in which a typical capacity vs. engine speed
diagram for a generator is shown. The capacity increases rapidly during the first 1300 rpm
engine speed but afterwards the increase slows down.). Alternating current generators offer
higher power at lower rotational speed compared to the direct-current ones having the same
weight. The alternator is usually a three-phase synchronous generator. The ratio of the belt
transmission is usually chosen in a way to enable the alternator the generation of 50% of the
rated power during idle run of the vehicle.
Figure A-1. Typical generator capacity depending on engine speed
Due to the fact that the wiring system in the bus demands a rather stable voltage level, the
alternator is equipped with a voltage regulator and an overload limiter.. This prevents
excessive current consumption. In hybrid buses the power generator could be a solution for
replacing for replacing the conventional alternators (see Figure A-2) for a typical alternator
installed in a bus), due to its increased efficiency and the current availability that is
independent of the rotational speed of the combustion engine. It takes energy from the
traction battery (high-voltage circuit) and converts it to 24 V, charging the accumulators. The
Vanner power generator has been constructed as a result of extensive development, testing
and validation. There are also some other solutions of DC/DC converters on the market (i.e.
manufacturing by ApeCOR or the Vicor Corporation) but it is the only generator which was
granted operational licence in combination with the Allison EP50 hybrid system thus the
further development will be done on the converter supplied by Vanner Inc..
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The figure A-2 shows the complete engine compartment layout. This is a standard solution
using alternators (electromechanical devices that produce electricity needed to power any
electrical devices in the bus and battery charging). The final amount of alternator depend on
the type of the bus and the equipment which determines the current request (load) coming
from the alternators.
As presented on figure A-2 alternators are driven by belt which is powered by bus engine.
Alternator is an electromechanical device (generator) that converts mechanical energy to
electrical energy (alternating current). It is used widely as a power source in buses and other
vehicles. To ensure co-operation with the battery, the alternator has a built-in rectifier and
voltage regulator.
Apart from the alternators many other bus systems are installed in the engine compartment
such as air conditioning compressor, heating devices, water pump, power steering pump,
filters, tanks, etc.
Figure A-2. The installation of alternators in a typical bus
The Vanner High Voltage DC-DC Converter (commonly referred to as HVDC in this
document) is an efficient and highly reliable component for converting high DC voltage,
present in hybrid drive systems, to the low voltage of 24 V, which is needed for auxiliary
batteries and auxiliary loads. The converter is designed to be the direct replacement of the
belt driven alternator leading to increased reliability and reduced maintenance costs.
A typical system includes a high voltage energy source (500 – 780 VDC), a Vanner converter
and a low voltage battery bank for auxiliary loads. The converter is equipped with a two pin
sealed connector - for integration into the vehicle’s high voltage interlock system - and a
fourteen pin sealed circular connector for interfacing to the CAN bus and vehicle I/O.
The High Voltage DC-DC Converter was also developed for being used in parallel with a belt
driven alternator system, which especially can be advantageous for additional low voltage
loads such as cooling fans. The specifications for this generator are written in Table 1 below:
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Table 1. General specification of High Power Generator
The diagram presenting the connection of the high-power generator to the wiring system of a
bus and a depiction of the high power generator design can be seen in Figure A-3.
Figure A-3. Scheme presenting the connection of the high-power generator to the wiring system of a bus
and the physical form of the Vanner generator (ref. [A-1]).
HCV Hybrid Commercial Vehicle – D2400.1, Rev_0
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A.1.
Installation of the high-power generator
Roof-mounted installation provides a cooler and cleaner environment than a standard
installation in the engine bay. Located near the battery, the Hybrid Beltless Alternator
(HVDC) is decoupled from the engine environment, eliminating the potential for thermal
events and allowing maximum installation flexibility and efficiency.
Fault protection devices must be installed between the DC-DC Converter and the power
source (traction battery). They should work as a fuse or circuit breaker properly rated to the
maximum tolerable DC current. This kind of design is in accordance with SAE, NEC and UL
standards for mobile power applications. Installation location is according to applicable
standards or within 18” of the battery.
Mounting Location:
The HVDC must be mounted on a flat horizontal surface supporting the device during
application. It cannot be mounted in a zero-clearance compartment because this may result
in overheating. A minimum of four inches distance should be allowed to the fan inlet and
outlet. Physical dimensions relevant to the mounting are shown in Figure A-4.
Figure A-4. Mounting details for the high power generator (dimensions in inches) 0
Wiring Sequence:
The HVDC is internally protected against reverse polarity. Therefore, the wiring sequence is
of no consequence.
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A.2.
Advantages resulting from the use of a power generator – fuel
savings
The Vanner HVDC uses DC Converter technology to replace the traditional alternator
hereby, achieving these benefits:
• 25-30% efficiency improvement compared to the traditional alternator technology (see
Figure A-5 and Figure A-6)
• Fuel economy improvements and reduced exhaust gas emissions. The engine load can
be reduced up to 60% by using the dc/dc converter instead of alternators.
• Stable DC power for all temperatures and engine speeds
• Precise and maintenance-free integrated voltage regulation
• Rugged, reliable performance - constructed to last at least until the bus mid-life and also
beyond
• Innovative design and installation location eliminates safety concerns and maintenance
problems associated with conventional alternators.
Figure A-5. System efficiency and electrical stress reduction benefits
Figure A-6. System efficiency mapping
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Figure A-6 presents the converter efficiency map depending on the current load and voltage
supplied to DC/DC converter.
Using a solid-state DC-DC converter as basis for the high power generator can significantly
reduce or even eliminate costly downtime and emergency road calls by removing the
following maintenance-intensive parts from the bus:
• Alternator
• V-Belts
• Voltage Regulator
• Pulleys and Idle Tensioner
• Hydraulic Lines and Fittings
A.3.
Cost Analysis
Costs have been calculated for a prototype unit and are expected to decrease in serial
production.
Component for HCV Project
Component
Supplier
Prototype costs [€]
High Power Generator
Vanner
3360
High Voltage cable
Moltec
1880
Vanner Software
Vanner
560
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B.
Electric Fans in Place of a Hydrostatic Fan for Engine Cooling
Combustion engines in buses, as well as in some other types of utility vehicles, demand
active cooling due to the positioning of the engine compartment. The cooling system in buses
has an extremely important function. It must react quickly and effectively on all kinds of
operational anomalies or changes. At high temperatures in summer the cooling system
protects the combustion engine from overheating, whereas during cold winter months it
guarantees optimum operating temperature. In addition, the heat generated by the
combustion engine is used to heat the passenger compartment of the bus.
Efficiency of the IC engine cooling system has a huge influence on the economy of the buses
operation. The time the engine needs to reach its correct operating temperature is closely
related to the fuel consumption.
The bus uses a forced circulation of the cooling liquid (water and glycol) which circulates in
the water jacket of the engine block and afterwards reaches the heaters and the radiator.
There are two circuits in the cooling system: the main circuit (engine – radiator, thermostat
open) and the bypass (engine – heaters, thermostat closed). The flow between these circuits
is controlled by the thermostat. Depending on the engine temperature, the thermostat closes
or opens the circulation paths, allowing the cooling liquid to enter the main circuit (radiator) or
the bypass.
In order to provide correct operation of the radiator, a sufficient amount of ambient cooling air
must be blown through it. This is guaranteed by the operation of a fan directly placed at the
radiator. In modern buses the radiator fan is preferentially powered by means of hydrostatic
systems rather than by direct mechanical drive. Such systems enable installing the radiator
independent from the location of combustion engine. In less advanced systems the radiator
must be close to the engine because the fan is either installed axially on a viscous clutch or it
is belt-powered directly by the engine. However, the solution utilising hydrostatics to power
the fan has also some disadvantages:

Considerably higher weight of the system

Difficulties related to the control of the system

The oil hydraulic medium is not desired due to possible leaks. Oil circulates in the
system under high pressure. Appropriate sealing needs to be provided.

Larger overall system dimensions

Low efficiency of the system (a large part of the energy is used to cool the oil which
can heat up considerably during operation)

Complexity of the system (engine, pump, tanks, hoses)

High failure frequency
Electric fans (more than one fan can be installed in the unit, which leads to high flexibility)
have the same advantage as the hydrostatic system concerning the flexibility of radiator
installation in relation to the combustion engine location but they do not have the
disadvantages of the hydrostatic system mentioned above.
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More specifically, they have the following significant advantages compared to the hydrostatic
fan:

They are lighter in weight.

They pose no difficulties related to the controlling of the fans, because it is
possible to operate them at various speed levels, independent from the
combustion engine’s rotational speed and it is also feasible to switch on and off
groups of fans independently

The system has high efficiency and the design is very simple.

No hydraulic fluids are present in the system.
B.1. Installation of the cooling system
Some of the advantages obtained from the electrification of the engine fan, like the reduction
in complexity and the space saving, can understood by comparing the installations of the
hydrostatic and the electric fan units along with their corresponding radiators and the cooling
piping.
For the hydrostatic fan, the radiator has a single large fan unit since the hydrostatic drive
does not allow efficient size reduction and duplication of fan drives. This has implications on
the dimensioning of the fan – radiator unit whereas, the electric fan unit provides some
flexibility in design. This can be seen by comparing these units in Figure B-1.
Figure B-1. Comparison of radiator - fan units: the hydrostatic drive (left) and the unit with the electric
fans (middle and right)
The flexibility in dimensioning the electrified fan – radiators units is available because they
are based on small electric fan modules, shown in Figure B-2.
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Figure B-2. Single electrically driven DC fan module
The system size and complexity of hydrostatic fan systems can be seen in depictions of
example installations of a complete cooling system shown in Figure B-3.
Figure B-3. Isolated rendering of the cooling system employing a hydrostatic driven fan
In contrast, the simplification and the reduced requirement of space in the complete cooling
system with electric fans can be appreciated from the depiction of the electric fan based
installation in Figure B-4. Figures B-3 and B-4 are rendered at roughly the same scale to
assist in the comparison of system size. Furthermore, the coolant tank and IC engine are
identical in the two configurations, providing a further size reference.
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Figure B-4. Isolated depiction of the complete cooling system installation with electric fans
The electrified cooling unit is generally thinner than the hydrostatic one by about 60% and
the thickness of complete electric cooler is 300 mm. The other dimensions (height and width)
are the same as on the hydrostatic cooler.
The electric fan units considered as shown in Table 3 are available off-the-shelf or with OEM
customisations and are more or less equivalent in performance and other operational
metrics. The main determining factors are air-moving efficiency and cost.
Table 2 - Comparison of electric fan models considered
Model:
ebm-pabst Mulfingen GmbH &
Co. KG
W3G 300-ER38-45
SPAL Automotive
VA01-BP90LL-79S
EMP Fill-11
Type:
brushless
brush motor
brushless
Fan diameter:
318 mm
305 mm
304,8mm
Nominal working
voltage / volt. range:
24V / 16 - 32V
24 V / 16 – 32 V
24 V / 9-32V
Air flow @ zero ΔP
3135 m /hr
3260 m /hr
-
Current at max. flow:
12,2 A (27,5V)
13,0 A (@26 V)
-
Fan unit mass:
2,5 kg
3.23 kg
3,86kg (~5kg fan +
controller)
Waterproofing level
IP24 KM
IP68
-
Op. temperature:
-40 °C – 85 °C
-40 °C – 110 °C
(100 °C continuous)
-40 °C – 95 °C
Op. lifetime:
40 000 hrs
20,000 hrs (VLL
version)
10 000 hrs
Unit price:
120€ /single fan
2800 € complete unit with 6 fans
130€ /single fan
5200€ complete unit
with 8 fans.
3
3
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The EBMPAST electric fans were chosen due to the best price-performance ratio. The
specifications of the electrically driven engine cooling fans selected for installation are given
in the Table 3 (EC = electronically controlled):
The selected fan unit includes electronic control, which automatically adjusts the current
distribution among the brushless motor coils to maintain the required position within the
operation/performance map (Figure B-5).
Table 3. Specifications of the electronically controlled fan
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Figure B-5. Performance map of the W3G 300-ER38-45 electric fan unit with respect to suction pressure
and achieved air flow rate (ref. [B-1])
B.1.1.
Advantages resulting from the use of electric engine fan – fuel-savings
The application of electric fans on the radiator results in lower fuel consumption, which is
mainly due to higher efficiency of energy conversion and the possibility to control the air flow
according to the cooling power needed at any given time. It also enables a better possibility
of controlling the fan’s rotational speed which is independent of the one of the combustion
engine.
The absence of the hydraulic drive of cooling fan leads to a weight saving in the electrified
fan-radiator system.
B.1.2.
Cost Analysis
The cost analysis has been evaluated for the solution with the best price-performance ratio.
Component for HCV Project
Component
Supplier
Prototype costs [€]
EBMPAPST electric fans (6pcs)
integrated with cooler
RAAL
2800€ complete system / 1
electric fan cost 120€
Electric fans driver
AND systemy
elektroniczne
120
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C.
C.1.
Potential for Electrification of the Crankcase Emissions Control
Scope of the review
The scope of emissions-related powertrain auxiliaries in WP2400 includes consideration of
the main exhaust after-treatment system and the crankcase emissions control system. The
electrification of the engine exhaust gas after-treatment system, focusing on the Diesel
Particulate Filter (DPF), is the subject of technology review (D2400.5) as well as prototype
construction (D2400.8) and testing efforts (D2400.9) within WP2400. The consideration of
crankcase emission control electrification was added to the scope of the WP as a paper
study that reviews existing crankcase emission control technologies and identifies available,
under development or potential electrically-driven systems.
C.2.
Crankcase emissions
Crankcase emissions are a result of the so-called engine blow-by, which consists of a
mixture of gases, droplets and/or solid particulates. Blow-by mainly originates from leakages
(due to the pressure) around the engine piston rings but can also have other causes such as
the turbocharger shaft [A-1]. With the tightening of the vehicle emissions legislation and the
overall needed reduction in engine exhaust emissions, engine blow-by emissions are
becoming an increasingly significant issue also occurring for commercial Diesel hybrid
vehicles. Additionally to the consideration as a part of the vehicle’s regulated emissions,
crankcase gases are often implicated in the so-called self-pollution1 problem. This is
especially a critical issue for passenger buses.
As a result of these considerations, a reduction of crankcase emissions is becoming more
important and widely practiced. Venting the crankcase to the atmosphere, even if with
emission control, is prohibited however simply venting the crankcase gases directly back to
the engine intake can be problematic. This is due to the formation of deposits from the
entrained oil droplets on intake valves and turbine blades, when a charge air compressor is
present. Furthermore, emission control systems have become increasingly sensitive to the
presence of oil droplets or their decomposition products in the exhaust gas.. This can lead to
serious service life reduction caused by ash accumulation or catalyst poisoning. Therefore,
crankcase gases must be cleaned somehow before this blow-by is directed back to the
engine intake.
A major differentiating factor of blow-by emissions compared to engine emissions is the
nature of the particles encountered and it is these particles that are the focus of blow-by
emissions control since the gaseous emissions generally do not survive reintroduction to the
combustion chamber. Whereas engine particulate emissions are mostly solid with a size
range of 0.005 – 1 micrometers, blow-by gas mainly exists of lube oil droplets (liquid) of
about 1 – 100 micrometers. This difference is particulate size has significant influence in the
filtering mechanism since inertial separation2 is possible for these sizes of particles. In fact,
1
Self-pollution refers to the deterioration of cabin air quality due to the ingress of the vehicle’s own emissions. In
older vehicles where open crankcase venting was allowed this was a frequently encountered problem especially
in vehicles with front-mounted engines.
2
Inertial separation refers to the mechanism of removing particles/droplets from an aerosol by promoting their
impact on a filter medium or other trapping structure. Inertial separation involves the use of high flow velocities
and tortuous flow paths such that the suspended aerosol particles/droplets deviate (due to centripetal
acceleration, i.e. their inertia) from the flow pathlines and impact on the surfaces of the porous structure they are
flowing through. The applicability of inertial separation depends on the size/shape and density of the aerosol
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inertial separation is the most frequently used mechanism in practice for oil mist separation
from blow-by gases.
C.3.
Existing commercial solutions for crankcase emissions control
The most common form of crankcase ventilation is the so-called positive crankcase
ventilation in which clean area is supplied to the crankcase in order to continuously remove
pollutants, water vapour and oil droplet aerosol that would otherwise contaminate the engine.
Conventional devices operate passively in that the crankcase ventilation system is not
separately powered nor actively controlled. Such passive crankcase breathers typically
depend on the vacuum level of the pre-turbo section of the intake manifold and may have a
one way valve system to prevent back flow into the crankcase. This makes their oil
separator’s effectiveness dependent on engine operation and introduces some (minor)
pumping losses for the engine. Therefore, the electrification of crankcase ventilation systems
would be pursued for reasons of improving performance in terms of oil mist separation (over
the entire engine operation map) and maintaining reduced crankcase pressure rather than
for energy efficiency gains as is the case for the other auxiliaries.
The primary requirement for crankcase emission control systems is the removal of oil spray
in the blow-by gases escaping past the piston rings (ref. [C-2]) both as a measure of
preventing pollution as well as in reducing lubricant oil loss. The size of the oil droplets
generally enables their removal via inertial separation, which is not possible for the Diesel
soot particulate matter because it primarily consists of nanoparticles that need to be treated
differently. Therefore, the main types of crankcase emission control devices are:

Separators existing of a porous medium on which the oil droplets impact and
gradually drain off towards a collection system that conducts the oil back to the
sump.

Separator systems based on the concepts of active or passive inertial droplet
separation by redesigning the flow pathways and/or incorporating elements that
increase centrifugal force on the particles (e.g. ref. [C-3]).

Devices that combine both methods to prevent an increase of crankcase pressure
during very high blow-by flow rates or in the event of excessive oil saturation of
the filter material (e.g. the Donaldson “Spiracle”™ system, ref. [C-5]).
In general, the operation of passive crankcase emission control systems is not associated
with high energy demand as long as they do not cause excessive pressure build-up in the
crankcase. In most cases the gaseous emissions present in the engine blow-by are not
treated contrary to engine exhaust emissions which are processed. Complete treatment of
crankcase emissions would entail potentially significant energy expenditure due to the
temperatures needed for catalytic treatment of hydrocarbons and carbon monoxide. In
practice, after oil droplet/particulate removal/reduction, the crankcase gas is vented back to
the engine intake so that hydrocarbon and carbon monoxide emissions are treated in the
cylinder. Due to this possibility not many crankcase emission control systems with an
additionally integrated power system have been implemented.
Although formally classified as passive devices, blow-by particle traps can induce nonnegligible parasitic power loss to the engine due to the pumping performed by the engine
intake section and due to potentially excessive crankcase pressures resulting from oil trap
particles as well as the flow conditions. For example, for nanoparticles such as Diesel soot, inertial separation
would only be effective ate rarefied (near vacuum) conditions and flow velocities approaching the speed of sound.
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clogging by the accumulated material. Therefore, electrification could aim at limiting
crankcase pressure levels to near atmospheric pressure while maintaining a high level of
separation function. At the present time, the only commercially pursued system is the
electrical cone stack separator by MAHLE (refs. [C-3], [C-4]). The principal of this device
(shown in Figure C 1.) is based on centrifugal acceleration of the incoming blow-by gases.
The centrifugal force is caused by a set of stacked cones which are rotated at high speed
(around 10000 rpm) by a brushless DC motor. The centrifugal acceleration of the oil droplets,
which then impact on the under-side of the cone surfaces, allows for very high separation
efficiency (specified at 98.5%) irrespective of the blow-by gas flow rate, since the device
does not depend of the blow-by flow rate to create inertial separation conditions. The power
consumption of this device is in the magnitude of 100 W for a typical system designed for
200 l/min of blow-by which can be typical for a 12 litre commercial vehicle engine.
The initial cost of the device is generally several times higher that of conventional/passive oil
separators for closed crankcase ventilation systems but this may be offset, in terms of total
cost of ownership, by the maintenance-free operation specified over a service life of 1.2
million km (there is no replaceable porous element for the oil trapping function).
Figure C-1. The electrical cone stack separator by MAHLE [C-4]
C.4.
Conclusions for the electrification of crankcase emission control
The motivation for electrification of crankcase emissions control differs from that of the
electrification of other vehicle auxiliaries considered within SP2000 in that energy efficiency
is not at all the main driving factor. Power consumption of passive/ conventional crankcase
breather oil separators generally is in the form of minor pumping losses induced by the use
of intake manifold vacuum for their operation. There is, however, the common motivation for
making the auxiliary operation independent of engine speed/load. Due to dependence on the
mechanism of inertial separation doe oil droplet removal, passive crankcase breather oil
traps are not very effective at lower blow-by flow rate or when engine intake manifold
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vacuum is less. From consideration of the only commercially available system, the conestack separator of MAHLE, it can be ascertained that electrification of the crankcase oil
separator is beneficial mainly for improving the effectiveness of the device in terms of oil
droplet separation efficiency as well as in decoupling this effectiveness from engine
operation. This improvement comes at a higher initial cost but due to the no-maintenance
operation may in fact be a cost-neutral component, over vehicle life time, in the transition to
electrified auxiliaries.
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D.
References
[A-1]
Owner’s Manual, Vanner High Voltage DC-DC Converter, Vanner Incorporated,
Hilliard, OH 43026, USA, 2008.
[B-1]
Automotive brushless DC fans for commercial vehicles, ver. 08/2008, p.26, ebmpapst Mulfingen GmbH & Co. KG, Mulfingen D74673, Germany.
[C-1]
EcoPoint Inc., ”Crankcase Ventilation”, revision 2009.01c,
http://www.dieselnet.com/tech/engine_crank.php
[C-2]. Kissner, G. and Ruppel, S.,”Highly Efficient Oil Separation Systems for Crankcase
Ventilation,” SAE Technical Paper 2009-01-0974, 20th of Apr 2009.
[C-3]. Enderich A. et al., “Highly Efficient Oil Separation Systems,” MTZ 04/2008, Volume
69, pp. 32-37.
[C-4]. MAHLE news and press information, “Optimization focus: filtration systems”,
Stuttgart, 2010. www.mahle.com
[C-5]
Donaldson Company, Inc., “Donaldson Spiracle(TM) ... A Crankcase Filtration System
(CFS),” Brochure No. F111122 (04/06), Minneapolis, MN, 2006.
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